1. Field of the Invention
This invention relates to the manufacture of cellulose fiber by a method comprising the spinning of continuous cellulose filaments from a solution of cellulose in an organic solvent, particularly an amine oxide solvent. Cellulose manufactured in this manner is known as lyocell and will hereafter be referred to as solvent-spun cellulose or lyocell. The invention particularly aims to provide a detection means to enable the presence of so-called "trash" on the formed continuous filaments to be detected at an appropriate stage in the manufacturing process.
2. Description of the Related Art
The manufacture of lyocell cellulose filaments is described, for example, in U.S. Pat. No. 4,416,698 the contents of which are incorporated herein by way of reference. This Patent discloses a method of producing cellulose filaments by dissolving the cellulose in a suitable solvent such as a tertiary amine N-oxide.
A hot solution of the cellulose is extruded or spun through a suitable die assembly including a jet to produce filamentary material which is passed into water to leach out the amine oxide solvent from the extruded filaments.
The production of artificially formed filaments of material by extruding or spinning a solution or liquid through a spinnerette to form the filaments is, of course, well known. Initially, relatively small numbers of individual filaments were prepared, which filaments were individually wound up for use as continuous filament material. This meant that the number of continuous filaments which needed to be produced was essentially dictated by the number of filaments which could be individually wound either before or after drying.
However, if fiber is produced as a tow or if fiber is produced as a staple fiber then different criteria apply to the number of filaments which can be produced at any one time. A tow essentially comprises a bundle of essentially parallel filaments which are not handled individually. Staple fiber essentially comprises a mass of short lengths of fiber. Staple fiber can be produced by the cutting of dry tow or it can be produced by forming a tow, cutting it whilst still wet, and drying the cut mass of staple fiber.
Because there is no need to handle individual filaments in the case of a tow product or a staple product, large numbers of filaments can be produced simultaneously.
One problem encountered in the commercial production of solvent-spun cellulose filamentary tows as described above is that "trash" can become attached to the filaments and so degrade their quality. "Trash" in this process is usually in the form of globules of cellulosic polymer formed from the "dope" or hot solution of cellulose. These globules have not been spun into filamentary form and they attach themselves to the filaments of the formed tow. "Trash" can also be formed by pieces of broken filamentary fiber. It can occur from time to time for a variety of reasons. For example, breakage may occur due to the tensions applied to the formed filaments at various points in the manufacturing process. Polymer globules may be caused, for example, by partial blockage of one or more of the spinning holes. Broken filaments, being undrawn, are much thicker than the drawn filaments.
Accordingly it is an object of the present invention to provide detection means in the manufacturing process to alert to the formation of "trash" on the tow of cellulose filaments.